Typically, a storage apparatus contains a controller comprising a cache memory and controls writing to a storage device in accordance with instructions from a host. Here, as a method of controlling a storage device, the following three control modes are mainly known. A first control mode is a method in which write processing is terminated at the time when data is written to a cache memory and the data in the cache memory is subsequently written to the storage device at a suitable time, and this mode is called write-after processing. Further, a second control mode is a method in which the processing is terminated after compulsorily writing the data to the storage device. In addition, the third control mode is a method in which data is written only to the cache memory and is called cache fast write (hereinafter also described as CFW: Cash Fast Write) processing and is used in writing generally used data such as a sort work file.
Meanwhile, nowadays, a storage apparatus logically converts physical storage areas which a multiplicity of storage devices comprise and provides the resulting logical storage areas to the host as virtual volumes. The host accesses the virtual volumes provided by the storage apparatus and performs data I/Os to/from the virtual volumes.
In addition, one such storage area logical conversion technology is hierarchical data management technology. With hierarchical management technology, a plurality of storage areas provided by a plurality of storage devices are managed as storage area groups for assigning virtual volumes. The storage area groups are categorized into a plurality of tiers according to the attributes of the storage devices. The plurality of tiers comprise, for example, an upper storage tier which comprises storage areas of high-speed and high-performance storage devices as well as a lower storage tier which comprises storage areas of low-speed and low-performance storage devices.
For example, PTL1 discloses a hierarchical data management technology which manages the frequencies of access by a host to each of the data written to the virtual volumes, migrates data of a high access frequency to a storage area provided by a high-speed and high-performance storage tier, and migrates data of a low access frequency to a storage area provided by a low-speed and low-performance storage tier. Cost-performance improvements for storage apparatuses are thus achievable.
Furthermore, according to PTL2, applications mounted on a host, virtual volumes from/to which the applications read and write data, and policies for associating storage tiers in which storage areas are assigned to the virtual volumes, and priority rankings, are managed. Further, in response to a write request from an application to write to a virtual volume, a storage area is assigned to the virtual volume from a storage tier with a higher priority ranking according to the corresponding policy. It is possible to prelimit the storage tier to which the storage area is assigned for each application when the application writes data to the virtual volume, and therefore a performance-stable operation for the virtual volumes can be realized.